The amount of epinephrine binding in rat adipocytes and hepatocytes changes with age although the specific affinity for the receptor is constant. We want to determine whether these changes correspond to a change in the geometry of receptor distribution. By scanning electron microscopy and transmission microscopy of replicas, we will observe the binding of a ferritin-labeled antagonist, alprenolol, as a marker for epinephrine receptors. We have begun to devise proper manipulations for hepatocytes in suspension for morphologic observation and the conjugated antagonist has been synthesized.